This invention relates generally to optical viewing devices. More particularly, this invention relates to a ring lens assembly for an optical viewing device for viewing remote locations which are difficult or impossible to directly access.
Optical viewing devices of the type described herein are well known and used in a variety of applications. For example, such devices are configured as borescopes and used to view or inspect the interior of remote cavities such as engine cylinders and the like. Borescopes thus find extensive utility in the automotive and aerospace industries. In the medical field, such optical viewing devices are configured as endoscopes or laparoscopes. Endoscopes (or laparoscopes) are well known medical instruments which are used to visualize the interior of a body cavity or hollow organ. Endoscopes are used in a variety of operative procedures including laparoscopic surgery where endoscopes are used to visually examine the peritoneal cavity.
Typical prior art optical viewing devices (e.g., borescopes and endoscopes) comprise three main sections including an objective lens followed by a relay lens followed by an eye piece. The relay lens section functions to transmit the image rays obtained by the objective lens along a preselected distance to the eye piece. The relay lens may consist of either a coherent fiber optical bundle or a series of lenses. When the relay lens section is comprised of a series of lenses, the lens series traditionally includes repeated units (e.g., three) with each unit comprising a symmetric arrangement of glass rods and lens groupings. Thus, in a prior art device having three relay sections, a total of six glass rods and associated lens groupings were required. These glass rods are used to preclude or lessen divergence of the image rays as they travel through the optical viewing device. Such glass rods must be of a high optical quality and therefore the glass rods lead to a relatively high manufacturing cost for each optical viewing device. Moreover, in certain prior art viewing devices, the objective lens and eye piece sections also contain glass rods leading to even higher manufacturing costs.
Illumination in the remote location to be viewed is required. A preferred method of transmitting illumination light is to use a bundle of optical fibers surrounding the outer circumference of the optical viewing device. These fibers are generally glass. The field of illumination should be of a size no less than the field of view (FOV) of the optical viewing device. Typically, the FOV may range between 30 to 75 degrees.
The method of illuminating the remote location to be viewed in both U.S. patent application Ser. No. 838,602 filed Feb. 19, 1992 assigned to the assignee hereof and incorporated herein by reference and in U.S. patent application Ser. No. 944,212 filed Sep. 11, 1992 assigned to the assignee hereof and incorporated herein by reference is accomplished by using the low cost plastic optical fibers. However, because plastic optical fibers have a relatively small numerical aperture and thus, a small field of illumination, the fibers are twisted (e.g., 15 degrees), the field of illumination is increased and may be tailored to match (or be no less than) the size of the field of view of the optical viewing device.
The devices of U.S. Ser. Nos. 838,602 and 944,212 further include a cleaning tube longitudinally along the length of the optical viewing the device. The cleaning tube is connected to a valve at one end thereof for injecting a cleaning fluid and protrudes outwardly from the other end thereof. The protruding end of the cleaning tube may inadvertantly puncture or otherwise damage tissue within a body cavity when the device is used as an endoscope or a laparoscope.